1. Field of the Invention
The present invention relates to a gas leak detection apparatus and detection method used in a gas meter or the like which is disposed in a gas supply line to a domestic dwelling and has a gas flow meter, and more particularly it relates to technology which enables the provision of higher advanced safety functions and services by detecting the presence of a gas leak during occurrence and continuation of the flow volume by a gas supply.
2. Description of the Related Art
A gas meter incorporating a gas flow meter is installed at the inlet port of the gas supply line to a domestic dwelling. The gas meter measures the gas flow volume passing through the gas supply line, and the measured gas flow volume is used to calculate a periodic gas billing amount. In addition to basic functions, such as measuring the gas flow volume, the gas meter also has a safety function for shutting off the gas supply when an abnormal state occurs. This safety function is a function which shuts off the gas by means of a shut-off valve provided in the gas flow path of the gas meter, in response to the detection of an abnormal usage state, for instance, if an earthquake is detected, if there is a gas leak or if the appliance is left without turned off, and the like.
FIG. 7 is a diagram showing the safe continuous use time settings employed in a shut-off function in the event that the safe continuous use time has been exceeded, which is one of the safety functions described above. This function is a function whereby, in cases where the occurrence of a gas flow has been detected and the gas flow is used continuously thereafter, then if the continuous use time has become excessively long, it is considered that an abnormal usage state of some kind, such as a gas leak, has occurred, and hence the gas is shut off.
As shown in FIG. 7, a large-scale water boiler which uses a large gas flow volume is only used continuously for approximately 30 minutes, whereas a stove which uses a small gas flow volume may be used continuously for a long period of time, and therefore based on this premise, the safe continuous use time is set to a short time when the gas flow volume is large and the safe continuous use time is set to a long time when the gas flow volume is small.
The gas meter judges that a gas appliance of some kind has started to be used, when a gas flow volume has occurred and or when the gas flow volume has changed into an increase, and based on this judgement, measures the time during which this flow rate continues. If this flow volume continues for a time exceeding the safe continuous use time shown in FIG. 7, then the gas meter shuts off the gas for safety reasons. Consequently, rather than identifying the gas appliance in use, a shut-off due to over-run of the safe continuous use time is implemented, on the basis of the used gas flow volume.
However, as shown in FIG. 7, a technique which measures the use time and compares same with a safe continuous use time is problematic in that it takes a long time to shut off the gas, even in the event of a gas leak.
On the other hand, in the prior art, a technique has also been proposed in which a gas leak is judged by comparison with patterns of flow volume change under reduced pressure or flow volume values measured in the past (see, for example, Japanese Patent Application Publication No. 2005-331373. However, even if a technique such as this is used, since a state of no change in the flow volume range or pattern continues both in the case of a gas leak and in the case of continuous use of a gas appliance which is not fitted with a governor (pressure regulator), such as cooking stove, then it has been difficult to distinguish between these two cases. In particular, when using an appliance which has been newly installed in a dwelling receiving a gas supply, since there is no data for comparison in relation to that appliance, then there has been a possibility of a gas leak being detected mistakenly.